1. Field of the Invention
This invention relates to a blood collector with a mechanism for allowing passage of air and preventing passage of air and blood. More particularly, it relates to such blood collector with a mechanism for allowing passage of air and preventing passage of air and blood which is especially used for blood inspection called blood gas analysis, wherein air removal and sealing process may be effected reliably while the process is checked visually.
2. Description of the Prior Art
In order to grasp the state of acid base balance or the lung function of a human body, blood inspection called blood gas analysis is effected, with a view to measurement of oxygen or carbon dioxide contents in the arterial blood or of p.sup.H or oxygen saturation values of the artery, and to qualitative analysis of the electrolyte components in the blood, such as HCO.sub.3.sup.-, Na.sup.+, K.sup.+ and Cl.sup.-.
In such blood gas analysis, measured results may be seriously affected by occasional mixture of air in the blood sample under examination. Therefore, it is of utmost importance to expel air from the collected blood sample.
To this end, a heparin solution is drawn as anticoagulant into the syringe of the collection container, prior to blood collection or the collection container is filled in advance with a heparin solution (see Japanese Utility Model Publication Nos. 49268/1978 or 42064/1977), to fill the dead space in the container or in the hypodermic needle with heparin solution.
The heparin solution used has the concentration generally in the order of 1000 units/ml, with water or physiological salt solution being used as diluent solvent. However, since this heparin solution is mixed with collected blood to dilute the blood, the results of blood gas analysis may be affected by fluctuations in the blood dilution degree by the heparin solution, resulting in accurate blood gas analysis.
It is therefore required to add heparin as an anticoagulant in a dried state into the syringe of the collection container to obviate the risk of blood dilution by the heparin solution, and to provide the blood collector with a separate mechanism for allowing air removal from the collector and sealing the collected blood from outside air. An example of such mechanism is described in the specification of U.S. Pat. No. 4,206,768.
According to said patent, the blood collector has an operating unit including a plunger and a gasket, said operating unit sliding in the collection vessel and closing the opened rear end of the container. The operating unit has a plastic thread or string which is inserted between the inner wall of the collection container and the outer wall of the gasket, whereby a gap connecting to outside is delimited in a portion of the rear inner end of the container. Air contained in the inside of the hypodermic needle and of the container is pushed up by the blood being collected and is discharged out of the container through the gap defined by the plastic string. After expulsion of air and completion of blood collection, the needle is removed from the blood vessel and the needle end is sealed as with rubber etc. The plunger is then rotated to take up the plastic string on the plunger. The rear end of the container may then be closed and sealed, with the gasket in intimate contact with the inner wall of the container. The blood collected may thus be sealed from outside air.
Such blood collector of the prior art has, however, certain defects in use and manufacture. Thus, in the case of a delay caused in extracting the hypodermic needle from the vein, the blood may leak out of the container by way of the string. Moreover, certain skill is required in blood collection because the pierced portion must be held with one hand while needle is removed from blood vessel and, in addition, plunger rotation as well as withdrawal of the collector must be made with one hand. Moreover, in manufacture of such blood collector, manual operation is required for attaching the plastic string between the gasket and the collector container. So the production en masse is a matter of considerable difficulties, because of painstaking labor involved in the manufacture, resulting in a rise in cost of the manufacturing process.